1. Field of the Invention
This invention relates to an integrated device for the creation of micropores in tissue, the harvesting of a biological fluid from the tissue, and the monitoring or analysis of a characteristic of the biological fluid, such as the concentration of an analyte.
2. Discussion of the Art
The prevalence of diabetes has been increasing markedly in the world. At this time, diagnosed diabetics represent approximately 3% of the population of the United States. It is believed that the total actual number of diabetics in the United States is over 16,000,000. Diabetes can lead to numerous complications, such as, for example, retinopathy, nephropathy, and neuropathy.
The most important factor for reducing diabetes-associated complications is the maintenance of an appropriate level of glucose in the bloodstream. Proper maintenance of the level of glucose in the bloodstream may prevent and even reverse many of the effects of diabetes.
Traditional glucose monitoring devices operate on the principle of taking blood from an individual by a variety of methods, such as by needle or lancet. An individual applies a drop a blood to a strip which contains chemistry that interacts with the blood. The strip is inserted into a blood-glucose meter for measurement of glucose concentration based on a change in reflectance of the strip.
These prior art glucose monitoring systems require that an individual have separately available a needle or lancet for extracting blood, strips carrying blood chemistry for creating a chemical reaction with respect to the glucose in the blood stream and changing color, and a blood-glucose meter for reading the change in color indicating the level of glucose in the bloodstream. The level of blood glucose, when measured by a glucose meter, is read from a strip carrying the blood chemistry through a well-known process.
Generally lancets comprise a blade and a trigger button. The blade has an acute end capable of piercing skin. By striking the trigger button, the acute end of the blade will pierce the skin, for example, of the finger. The finger lancet is primarily used to obtain small volumes of blood, i. e., less than 1 mL. Diabetics use the finger lancet to obtain volumes of blood less than 25 μL for glucose analysis. There are many small blood vessels in each finger so that a finger can be squeezed to produce a larger drop of blood. In addition, the finger is one of the most sensitive parts of the body; accordingly, the finger lancet causes more pain than what would be experienced by extracting blood via a lancet at a different body site. The finger lancet presents another problem due to the limited area available on the fingers. Diabetics typically monitor blood glucose levels two to four times per day, and consequently must repeat lancing of areas that are still healing. Because fingers are sensitive to pain, there has been a recent trend to subject the arm to blood sampling. See, for example, U.S. Pat. No. 4,653,513 which discloses a device comprising a cylindrical housing, a lancet support, and a gasket or flexible portion slidably accommodated in the housing. Springs retract the lancet support to thereby reduce air pressure in the housing so that it automatically sucks a blood sample immediately after a lancet pierces the skin.
There are other technologies being developed to provide an alternative to the conventional blood glucose monitoring procedures. One such technology involves measuring the level of glucose in interstitial fluid. In order to obtain samples of interstitial fluid, the barrier function of the stratum corneum must be overcome.
U.S. patent application Ser. No. 08/776,863 entitled “Microporation Of Human Skin For Drug Delivery and Monitoring Applications,” filed Feb. 7, 1997, to Eppstein et al., discloses a method of ablating the stratum corneum to form at least one micropore comprising the steps of treating a selected area of the stratum corneum with an effective amount of dye that exhibits strong absorption over the emission range of a pulsed light source and thermally ablating the stratum corneum by optically heating the dye. Heat is conductively transferred by the dye to the stratum comeum to elevate the temperature of tissue-bound water and other vaporizable substances in the selected area above the vaporization point of water and other vaporizable substances. Another microporation technique disclosed in that application which involves the use of a solid thermal probe that is applied directly to the tissue. To the subject, these techniques are much less painful than using a lancet, if not completely painless.
There is room for improving on these glucose monitoring technologies. In particular, it is desirable to integrate several functions of the glucose monitoring procedure onto a single device. Preferably, this device would facilitate the harvesting of a biological fluid, such as interstitial fluid, the collection and management of the interstitial fluid, and the analysis of the interstitial fluid to determine a measure of a characteristic of the fluid, such as glucose level.